A conventionally known sheet transport apparatus sequentially transports originals in sheet form (hereinafter referred to as sheets) as reading object placed on a sheet supply tray to a reading section of an image reading apparatus, and then ejects the sheets to an eject tray. Further, by providing the sheet transport apparatus to an image reading apparatus, the image reading apparatus can realize efficient reading of sheets. Further, by providing to an image forming apparatus, the image reading apparatus provided with the sheet transport apparatus as described above, the image forming apparatus can realize efficient image formation.
Further, in accordance with recent advancement of digital technology, speed for reading sheets, speed for converting the read sheets into electronic data, and speed for forming images from the electronic data have improved. This realizes prompt processing of sheets in larger quantities.
Further, in accordance with technological advancement of the sheet transport apparatus, the type of sheets that can be transported has diversified. For example, it is possible to perform processing for reading sheets even if sheets placed on the sheet supply tray have different sheet lengths in a transporting direction.
When a group of sheets in which sheets having different sheet lengths in the sheet transporting direction are mixed is read as described above, the following problems will occur. The problems will be explained with reference to FIGS. 34 and 35. Note that, in the following explanation, the sheet length in the sheet transporting direction will be simply described as sheet length.
FIG. 34 is a cross-sectional view of a sheet transport apparatus 101 that sequentially transports sheets in order from the bottom, in a case where two sheets (P1 and P2) respectively having different sheet lengths are placed on a sheet supply tray 102. Further, FIG. 35 is a cross-sectional view of the sheet transport apparatus 101 in a case where the two sheets (P1 and P2) respectively having different sheet lengths are ejected to an eject tray 103.
As shown in FIGS. 34 and 35, when the two sheets (P1 and P2) respectively having different sheet lengths are read in order from the lower sheet P2 (when read in order from the later page), the sheets (P1 and P2) are ejected to the eject tray 103 in such a manner the page order of the sheets is retained.
However, there arises a problem that leading edges of the sheets (P1 and P2) are not aligned with each other, as shown in FIG. 35. Note that, the leading edge of the sheet P1 is indicated by the white triangle mark and the leading edge of the sheet P2 is indicated by the black triangle mark in FIGS. 34 and 35.
In particular, if sheets having different sheet lengths are kept in a file, for example, the sheets are generally kept in such a manner that left edges of the sheets as a reference are aligned. Accordingly, after taking out the read sheets (P1 and P2) from the eject tray 103, the user is required to align the leading edges of the sheets (P1 and P2).
Further, in a sheet transport apparatus that sequentially transports sheets in order from an upper sheet, the sheets are ejected to the eject tray after the page order of the sheets is reversed.
Moreover, the problem that the leading edges are not aligned occurs not only when the sheets are read, but also occurs in an image forming apparatus provided with an inkjet line head 104′ as shown in FIG. 36. Namely, in a case where information is recorded using the inkjet line head 104′ on recording sheets (P1′ and P2′) transported by a sheet transport apparatus 101′ and the recorded sheets (P1′ and P2″) are ejected to an eject tray 103′, the leading edges of the sheets are not aligned if the sheets (P1″ and P2′) have different sheet lengths.
Further, the problem that the leading edges are not aligned as described above may occur in a case where the sheets to be transported include a sheet P2″ with an index (tab) (namely, sheet partly having a protrusion), as shown in FIG. 42.
FIG. 43 is a cross-sectional view of the sheet transport apparatus 101 in a case where a normal sheet P1″ without a protrusion and the sheet P2″ with an index are placed on the sheet supply tray 102. Note that, hereinafter the normal sheet P1″ without a protrusion is simply referred to as sheet P1″. Further, FIG. 44 is a cross-sectional view of the sheet transport apparatus 101 in a case where the sheet P1″ and the sheet P2″ with an index are ejected to the eject tray 103.
In this case, when the sheet P1″ and the sheet P2″ with an index are sequentially read in order from the sheet P2″ with an index on the lower side as shown in FIGS. 43 and 44, the sheets (P1″ and P2″) are ejected to the eject tray 103 in such a manner that the page order of the sheets (P1″ and P2″) is retained.
However, there arises a problem that the leading edges of the sheets (P1″ and P2″) are not aligned, as shown in FIG. 44. This is because the index section of the sheet P2″ with an index is on the side of a placing reference of the eject tray 103. Note that, the leading edge of the sheet P1 is indicated by the white triangle mark and the leading edge of the sheet P2 is indicated by the black triangle mark in FIGS. 43 and 44.
Further, FIG. 46 is a cross-sectional view of a sheet transport apparatus 101″ that sequentially transports sheets in order from an upper sheet, in a case where the sheet P1″ and the sheet P2″ with an index are placed on a sheet supply tray 102″. Further, FIG. 47 is a cross-sectional view of the sheet transport apparatus 101″ in a case where the sheet P1″ and the sheet P2″ with an index are ejected to an eject tray 103″.
As shown in FIGS. 46 and 47, when the sheets (P1″ and P2″) are read in order from the upper sheet P1″ (when read in order from the former page), the sheets (P1″ and P2″) are ejected to the eject tray 103″ in such a manner that the page order of the sheets is retained.
However, in the sheet transport apparatus 101″, there also arises the problem that the leading edges of the sheets (P1″ and P2″) are not aligned with each other, as shown in FIG. 47. Note that, the leading edge of the sheet P1″ is indicated by the white triangle mark and the leading edge of the sheet P2″ is indicated by the black triangle mark in FIGS. 46 and 47.
Further, the sheets may be transported in such a manner that the edges of the sheets on the index side are set as the leading edges. In this case, however, the following problems will occur.
A sheet with an index has a protrusion on a part of the sheet, as described above. Further, a position of the protrusion may differ from one sheet to another. Therefore if the sheets are transported with the index side being set as the leading edges, the sheets get easily caught in a transport path. As a result, the sheets may be transported in an inclined manner (in a slanted state), or a so-called jam may occur. Further, since the sheets are transported with the index side being set as the leading edges, the slanted state cannot be corrected even if resist means is used.
Therefore there is a problem that it is difficult to achieve the transporting correctly and stably, compared with a case where only normal sheets with no protrusion are transported.
Accordingly, for example, Patent Document 1 (Japanese Unexamined Patent Publication No. 3-147682 (Katajima, et al. 3-147682), published on Jun. 24, 1991) describes a sheet transport apparatus that can align leading edges of sheets after the sheets are read and ejected to a tray, even if the sheets have different sizes (sheet lengths).
The sheet transport apparatus 111 described in Patent Document 1 performs the following processing when transporting sheets having different sheet lengths. First, a pickup roller picks up a lowermost sheet PZ. Next, the sheet PZ is transported to a predetermined sheet reading position through a first path 113. After the sheet is read, the sheet PZ is ejected to a sheet supply tray 112 through a second path 114.
After the sheet PZ is ejected to the sheet supply tray 112, a lowermost sheet PZ−1 is ejected to the sheet supply tray 112 through a path similar to that of the sheet PZ. Here, the sheet PZ−1 is placed on the sheet PZ. Then, similar processing is performed with respect to the other sheets.
By ejecting the sheets to the sheet supply tray 112 as described above, it is possible to align the leading edges of the ejected sheets as shown in FIG. 37. With this, the user does not need to align the leading edges.
Further, Patent Document 2 (Japanese Unexamined Patent Publication No. 8-268569, (Tokukaihei 8-268569), published on Oct. 15, 1996) discloses a sheet transport apparatus that can change a destination to which sheets having different sizes are ejected, according to size, after the sheets are copied.
Further, Patent Document 3 (Japanese Unexamined Patent Publication No. 4-55259, (Tokukaihei 4-55259), published on Feb. 21, 1992) discloses a facsimile apparatus that can switch the direction of outputting sheets, so as to select either a structure that does not change the outputting direction or a structure that reverses the outputting direction.
Further, Patent Document 4 (Japanese Unexamined Patent Publication No. 9-258615, (Tokukaihei 9-258615), published on Oct. 3, 1997) discloses an image forming apparatus that supplies a sheet with a tab and copies an original onto the supplied sheet when the image forming apparatus judges that the original to be copied has a tab.
However, in a case of Patent Document 1 where the sheet transport apparatus 111 sequentially reads large quantities of sheets placed on the sheet supply tray 112, the following problems will occur.
Namely, when the pickup roller attempts to sequentially pick up the sheets one sheet at a time in order from the later page, if large quantities of sheets are stacked on a sheet to be picked up, the sheet to be picked up is subject to the weight of the other sheets. Therefore it is difficult to pick up the desired sheet. Namely, in this case, the pickup roller may simultaneously pick up a plurality of sheets.
Further, if the arrangement of the sheet transport apparatus 111 is modified so that the pickup roller of the sheet transport apparatus 111 sequentially picks up the sheets one sheet at a time in order from the former page, the sheets are ejected to the sheet eject tray 112 after the page order of the sheets is reversed.
Moreover, in order to prevent the page order of the sheets from being reversed as described above, it is necessary to eject a sheet under the sheet that has been already ejected to the sheet supply tray 112. Therefore the sheet transport apparatus needs to be separately provided with a complicated mechanism for lifting the already ejected sheet from the sheet supply tray 112 each time a sheet is ejected, for example. If such a complicated mechanism is provided, it is difficult to improve the reading speed.
Further, since the read sheets are ejected to the sheet supply tray 112, sheet(s) are always placed on the sheet supply tray 112. Therefore the user cannot easily judge whether or not the reading of all the sheets has been complete.
Further, if the description in Patent Document 1 is applied to the case where the inkjet line head 104′ is used to record information on the recording sheets (P1 and P2), similar problems as in the case of the reading of the sheets occur such that a plurality of sheets are simultaneously picked up.